Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
It may be useful to alter a person's circadian rhythm or “sleep cycle” for reasons such as jet lag and adjustment to non-traditional work shifts. A person's circadian rhythm is principally governed by the suprachiasmatic nucleus (SCN), which is a small region within the brain's hypothalamus. Previous methods for altering a person's circadian rhythm have generally involved direct stimulation of the light-sensitive protein melanopsin within intrinsically photosensitive retinal ganglion cells (ipRGCs) that make up about 1% of retinal ganglion cells within the retina. It is thought that illumination of the retina with blue light (e.g., peak wavelength of about 480 nanometers) causes melanopsin excited within a person's ipRGCs to stimulate the SCN via neural pathways, thereby altering the person's circadian rhythm (e.g., delaying the onset of tiredness). However, due to the ipRGCs' relatively low photosensitivity, their relatively sparse presence within the retina, and slow photoactive response, such methods may undesirably involve illuminating the retina with intensities that are unpleasant or even painful, for relatively long periods of time.